ISA Server 2004 System Policy

Microsoft Internet Security and Acceleration (ISA) Server 2004 includes a default system policy configuration, which allows use of services commonly required for the network infrastructure to function properly.

In general, from a security perspective, we strongly recommend that you configure the system policy so that access to services that are not required to manage your network is not allowed. After installation, carefully review the system policy rules configured. Similarly, after you perform major administration tasks, review the system policy configuration again.

This document describes services that are enabled by system policy rules.

When you install ISA Server, basic network services are enabled. After installation, ISA Server can access name resolution servers and time synchronization services on the Internal network.

If the network services are available on a different network, you should modify the applicable configuration group sources to apply to the specific network. For example, suppose the DHCP server is not located on the Internal network, but on a perimeter network. Modify the source for the DHCP configuration group to apply to that perimeter network.

You can modify the system policy, so that only particular computers on the Internal network can be accessed. Alternatively, you can add additional networks, if the services are found elsewhere.

The following table shows the system policy rules that apply to network services.

Configuration group

Rule name

Rule description

DHCP

Allow DHCP requests from ISA Server to Internal

Allow DHCP replies from DHCP servers to ISA Server

Allows the ISA Server computer to access the Internal network using the DHCP (reply) and DHCP (request) protocols.

DNS

Allow DNS from ISA Server to selected servers

Allows the ISA Server computer to access all networks using the DNS protocol.

NTP

Allow NTP from ISA Server to trusted NTP servers

Allows the ISA Server computer to access the Internal network using the NTP (UDP) protocol.

DHCP Services

If your DHCP server is not located on the Internal network, you will have to modify the system policy rule, so that it applies to the network on which the DHCP server is located. For example, if the DHCP server is located on the External network, perform the following steps.

Click Start, point to All Programs, point to Microsoft ISA Server, and then click ISA Server Management.

In the System Policy Editor, in the Configuration Groups tree, click DHCP.

On the From tab, click Add.

In Add Network Entities , select a network object.

Note:

We recommend that, if you know the IP address of the DHCP server, create a computer set with just that IP address and select that computer set. We strongly recommend this when the DHCP server is located on an untrusted network.

One of the fundamental capabilities of ISA Server is the ability to apply a firewall policy to specific users. To authenticate users, however, ISA Server must be able to communicate with the authentication servers. For this reason, by default, ISA Server can communicate with Active Directory servers (for Windows authentication) and with RADIUS servers located on the Internal network.

The following table shows the system policy rules that apply to authentication services.

DCOM

If you require use of the DCOM protocol—for example, to remotely manage the ISA Server computer—be sure that you do not enable Enforce strict RPC compliance. To verify that Enforce strict RPC compliance is not selected, perform the following steps.

Click Start, point to All Programs, point to Microsoft ISA Server, and then click ISA Server Management.

In the System Policy Editor, in the Configuration Groups tree, click Active Directory.

On the General tab, verify that Enable is not selected.

Note:

When you disable the Active Directory system policy configuration group, access to all LDAP protocols is effectively disabled. If you require the LDAP protocols, create an access rule allowing use of these protocols.

Repeat steps 4 and 5 for the RADIUS configuration group.

Note:

If you require only Windows authentication, be sure to configure the system policy, disabling use of all other authentication mechanisms.

RSA SecurID Authentication Services

Communication with RSA SecurID authentication servers is not enabled by default. If your firewall policy requires RSA SecurID authentication, be sure to enable this configuration group.

CRL Authentication Services

Certificate revocation lists (CRLs) cannot be downloaded by default. This is because the CRL Download configuration group is not enabled by default. To enable CRL download, perform the following steps.

Click Start, point to All Programs, point to Microsoft ISA Server, and then click ISA Server Management.

Often, you will manage ISA Server from a remote computer. Carefully determine which remote computers are allowed to manage and monitor ISA Server. The following table shows the system policy rules that should be configured.

Configuration group

Rule name

Rule description

Microsoft Management Console

Allow remote management from selected computers using MMC

Allow MS Firewall Control communication to selected computers

Allows computers in the Remote Management Computers computer set to access the ISA Server computer using the MS Firewall Control and RPC (all interfaces) protocols.

Terminal server

Allow remote management from selected computers using Terminal Server

Allows computers in the Remote Management Computers computer set to access the ISA Server computer using the RDP (Terminal Services) protocol.

ICMP (Ping)

Allow ICMP (PING) requests from selected computers to ISA Server

Allows computers in the Remote Management Computers computer set to access the ISA Server computer using the Ping protocol, and vice versa.

By default, the system policy rules allowing remote management of ISA Server are enabled. ISA Server can be managed by running a remote Microsoft Management Console (MMC) snap-in, or by using Terminal Services.

By default, these rules apply to the built-in Remote Management Computers computer set. When you install ISA Server, this empty computer set is created. Add to this empty computer set all computers that will remotely manage ISA Server. Until you do so, remote management is effectively not available from any computer.

Note:

Limit remote management to specific computers by configuring the system policy rules to apply only to specific IP addresses.

To enable remote management, perform the following steps.

Click Start, point to All Programs, point to Microsoft ISA Server, and then click ISA Server Management.

If you installed the Firewall Client Share component when you installed ISA Server, the Firewall Client Installation Share configuration group is enabled, by default. All computers on the Internal network can access the shared folder. The following table shows the system policy configuration group (and rule) that is enabled.

Allows computers on the Internal network to access the ISA Server computer using various Microsoft CIFS and NetBIOS protocols. When you enable this rule, access is allowed to the ISA Server computer using SMB from any network or computer specified. Access is not limited only to the Firewall Client installation shared folder.

If you did not install the Firewall Client Share component, this configuration group is not enabled.

In addition, the following diagnostic service is not enabled by default: HTTP Connectivity Verifiers.

When you create a connectivity verifier, the HTTP Connectivity Verifiers configuration group is enabled, allowing the Local Host network to use HTTP or HTTPS to access computers on any other network. The following table describes the HTTP Connectivity Verifiers configuration group.

Configuration group

Rule name

Rule description

HTTP Connectivity Verifiers

Allow HTTP/HTTPS from firewall to all networks, for HTTP connectivity verifiers

Allows the ISA Server computer to check for connectivity by sending HTTP GET requests to the specified computer.

We recommend that you limit this access to the specific computers whose connectivity you want to verify. To limit this access, perform the following steps.

Click Start, point to All Programs, point to Microsoft ISA Server, and then click ISA Server Management.

In the System Policy Editor, in the Configuration Groups tree, click HTTP Connectivity Verifiers.

On the To tab, click All Networks (and Local Host) and then click Remove.

Click Add and then select the network entities whose connectivity you want to verify. All HTTP traffic will be allowed from the Local Host network (the ISA Server computer) to network entities listed on the To tab.

By default, the SMTP configuration group is enabled, allowing SMTP communication from ISA Server to computers on the Internal network. This is required, for example, when you want to send alert information in an e-mail message. The following table describes the SMTP configuration group.

Configuration group

Rule name

Rule description

SMTP

Allow SMTP from ISA Server to trusted servers

Allows the ISA Server computer to access the Internal network using the SMTP protocol.

The default system policy allows HTTP and HTTPS access from the Local Host network (that is, the ISA Server computer) to the microsoft.com Web site. This is required for a few reasons:

Error reporting (as described in the Diagnostic Services section)

Access to useful documentation on the ISA Server Web site and on other related Web sites

By default, the Allowed Sites configuration group is enabled, allowing ISA Server to access content on specific sites that belong to the System Policy Allowed Sites domain name set. The following table describes the Allowed Sites configuration group.

Configuration group

Rule name

Rule description

Allowed Sites

Allow HTTP/HTTPS requests from ISA Server to specified sites

Allows the ISA Server computer to access members of the System Policy Allowed Sites URL set using HTTP and HTTPS protocols.

This URL set includes various Microsoft Web sites, by default. You can modify the domain name set to include additional Web sites, which ISA Server will be allowed to access.

To modify the URL set to include additional Web sites, perform the following steps.

Click Start, point to All Programs, point to Microsoft ISA Server, and then click ISA Server Management.